Silicon thermo-optic variable optical attenuators based on Mach-Zehnder interference structures

We experimentally demonstrate silicon variable optical attenuators (VOAs) based on thermally tunable Mach-Zehnder interferometers (MZIs). Thermo-optic tuning is enabled by a silicon resistive micro-heater positioned beside the MZI arm. Experimental results reveal that the maximum attenuation is around 30 dB with 50 mW power consumption. Compared with the p-i-n diode based VOA, the MZI-VOA is more power efficient and compact. The influence of MZI arm length on the performance of MZI-VOA is also investigated. The maximum attenuation voltage for the MZI-VOA with a 50 μm long arm length is around 6.6 V.